Another thing to consider. My 5 year old CX-5 has 70,000 miles now. It has cost me only for routine maintenance and replacement of wear and tear items (tires, brakes, etc.). I expect a long lifetime ahead for this vehicle. 30 years ago however, I would be looking at a replacement vehicle by now since I would know that major expenses were going to start happening and reliability would start to tank. In other words, to my mind, a new vehicle is now more of a want than a necessity and I would expect new vehicle demand to be less because of that.
I always paid cash for my cars, drove them for a few years, then sold them for at least what I initially paid...many times for more than that. By buying used, I also saved on insurance and property taxes.
For me, the problem arises when you get so many miles on a vehicle that you hesitate to drive it too far from home. I got to that point with my truck (135,000). Vacation trips in it were out of the question, and rental cars just add aggravation and time to going anywhere (and where I am, the nearest rental car place is nearly an hour away). Impromptu trips are out of the question.
Last year I started to look for low-mileage used, but they hold their resale value so well (continued Cash for Clunkers impact?), that after factoring in Dealer Financing specials, I bought my new CX-5 for not much more per month that I could have purchased used. As silly as it seems, having this new car has freed me up. I've retired to a rural area with almost no traffic, and can actually enjoy driving again and take road trips just for the heck of it. I go to the beach about 160 miles away and don't give a second thought to breaking down somewhere. It doesn't take a major failure to leave you stranded, and gone are the days that carrying an extra set of points & condenser and a toolbox in the trunk is gonna get you through most emergencies.
Of course, it's all academic if you don't have the money.
To your other point, it is interesting that we used to pop the champagne if we were lucky enough to hit 100,000 on a car and not measure oil consumption in Quarts-per-Tank (I've had 2 FlatHead Six <s>mosquito foggers</s> cars). These days, longevity is pretty much taken for granted, even in low-end cars. I recently saw a single owner CR-V for sale that had over 400,000 on it.
It would be informative to see the historical stats for the percentage of vehicles on the road broken down by age. Understanding what people
are doing different these days would help.